Safety control system for fuel burners



March 26, 1946. s. G. EsKlN Erm. 2,397,311

Y SAFETY CONTROL SYSTEMS FOR FUEL BURNERS Filed Dec. 8., 1945 lmea'l n/ Purge Sal/ich 60 llllllllll\ I T20 715" x C) l J2 HEL? ATTORNEYv Patented Mai'. 26, 1946 SAFETY CONTROL SYSTEM FOR FUEL BUR NERS

Samuel G. Eskin and, Charles K. Strobel, Pitts-l bur-gh; Pa., assignors to Robertshaw Thermostat Company, Youngwood, Pa., r" corporation of Pennsylvania Application December s, 1943, serial No. 513,3'88

12 Claims.

This invention relates to safety control apparatus for fuel burners and, more particularly, to electrically operated controls therefor.

An object of the invention is to utilize electrical igniting means for the burner and automatically deenergize such means vuponl establishment of normal running conditions of the burner.

Another object of the invention is to reenergize the igniting means after operation of the safety control to provide a recycling system.

Anotherobject of the invenion is to delay reenergization of the igniting means until the vicinity of the burner has been purged of unburned fuel.

A still further object of the invention is to discontinue burner operation in the event of electric power failure or the occurrence of an open circuit in the electrical system. y

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing whiclris a schematic view of a safety control apparatus for a gaseous fuel burner embodying this invention.

Referring more in detail to the drawing, a gaseous fuel burner Ill is supplied with fuel from a main fuel pipe I2. The fuel supply is controlled by a main valve I4 which, in this instance, is adapted for manual operation but which may be arranged for thermostatic operation if desired.

Preferably, a double-pole main switch for the electric circuit to be described isvincluded in the main valve I4 and is arranged toestablish the electrical circuit of the apparatus whenever the main valve is opened. Interposed in the fuel supply pipe I2 between the main valve I4 and the burner I is an electromagnetic gas valve I6 of any suitable type which may be arranged, as in this instance, to be opened by energization of the electromagnet and closed by gravity upon deenergization thereof.

. A pilot burner I8 is supplied with fuel from a `conduit 20 connected to the main valfe I4 to receive fuel from thesupply pipe I2 when the main valve is opened. The fuel flowing from the pilot burner is adapted to be ignited by an electric.

' (C1. 15s-2s) double pole switch are connected by wires 28-86 to the primary of a transformer 32.

Operation of the electromagnetic valve I6 and ignition means 22 is controlled by a control relay' 34. This relay may include a magnetizable core 36 having the usual energizing coil 38 associated therewith and is shown as adapted to attract a pair of movable armature members 4I) and 42 when suitably energized. The armatures 40 and l0 42 maybe mounted for movement toward and away from the core 86 and adapted to return to a normal or unattracted position. by gravity. spring or other means (not shown). i

In the normal position of the armature 42, that l5 is, when the relay operating means is deenergized, engagement is made by a contact 44 thereonwith a fixed contact 46. In addition to the contact 44, the armature 42 carries on the opposite side thereof a contact 48 which is adapted to engage with a fixed contact 50 when the armature 42 moves from normal to attracted position. It will be apparent that upon such movement contacts 44-46 become disengaged. In similar manner, armature carries contact 52 26 which is adapted for engagement with a -fixed contact 54 in the attracted position of this armature. Contact 52 is, however, the only contact carried by armature 48 as distinct from armature 42 which, as described, carries two contacts. A heat responsive or flame sensitive element 56 is positioned to be exposed to the ame of the pilot burner I8 for causing operation of the relay 34 to move the armatures thereof from one position to the other. The flame sensitive element 56 may take the form of a coil of wire ofmaterial having normally a, relatively low resistance and a positive temperature coeiiicient of resistance. Suchl devices commonly termed ballast resis tors are thermally responsive to they passage of. current therethrough but, in this embodiment, the element 56 is primarily responsive to the heat of the pilot burner flame. Accordingly, it will be understood that it is the variation in resistance in response to the flame of the pilot 'closure of the electromagnetic valve I6. The

timing means for the switch 60 comprises a bimetal element 62 carrying a contact 64 which is adapted to move therewith and vengage a fixed contact 66 when the bimetal element 62 is unheated. The arrangement provides that these4 contacts 64-66- become disengaged whenever the bimetal is sumciently heated. y l

Adjustment of the igniter current value in .the system may be obtained by the provision of contacts `52-1'5'4 and 48--0-50,l respectively. Thus 'the circuit of pilot signal light 10 is discontinued by opening lof contacts 44-46 and the following additional circuits are established.

One circuit comprises Ithe secondary of the transformer .32, wire |06, regulating resistor 88,

wire |08, ignition means 22, wire IIO, contacts 66-64 of purge bimetal switch 60, wire I|2, relay contacts 50-48, relay armature 42 and wires |02--I04 back to the secondary of the transformer 32. The energization of the circuit just I described causes the ignition/'means 224 to be ena regulating resistor 68 which is preferably of fixed impedance value. A pilot signal lamp 10 may be included to aord visual indication of normal running operation of the system. In order that the flow of fuel in the main burner I0 will be shut oiin case of electric power fail- `ure or an open circuit in the electrical system of the apparatus. safety switch means are provided to perform this function. This means may take the form of a second thermally operated switch 14 comprising a bimetal element 16 car-- rying a contact 18 which is adapted to' 'move therewith and engage a fixed contact 80 when the bimetal element 16 is heated. In this arrangement it is provided that these contacts 18- 80 become disengaged whenever the ybimetal ris unheated. A limiting resistor 82 of fixed impedance value is provided for a purpose which will be apparent hereinafter.

` The apparatus so far described is shown Vin the drawing in the normal. running position of the main burner I0, the electromagnetic valve I6 being energized andthe ignition meansv 22 deenergized. At the start -of operation to obtain this running positionthe thermally responsive circuit elements are cold; the control relay 34 occupies the normal position shown; the contacts 84--66of the purge bimetal switch 60 are closed;

while'the contacts 18-80 of the safety bimetal valve |4 permits' fuel to,l

ergized to ignite the fuel flowing from the pilot burner I8.

The heater coil 84 of the safety bimetal switch 114 whichy is included in the first circuit described causes contacts 18-88 of this switch to close shortly after the main switch of valve I4 is closed. Thus, a circuit is established from the secondary of the transformer 32, wire |06, wire H4, safety bimetalswitch contacts'18-80, limiting resistor 82, wire ||6, relay contacts 54-52, relay armature 40, wire ||8 and wire |04 4back to the secondary of the transformer 32. It will be apparent that the purpose of the limiting resistor 82` is to prevent a short-circuit on the transformerr secondary vas contacts 52-54 are closed at the same time as contacts 18-80 are closed. The circuit so established-will short-circuit the electromagnetic valve I6 as one terminal thereof is connected by a Wire |20 to wire |04 and the other v,

terminal thereof is connected by a wire |22, through a heater coil |24 for the purge bimetal switch 60 and a wire |26 to wire I I0.

As the ignition circuit is established through the closed contacts 48-50 of relay 34 and closed contacts 64-66 of the yet' unheated purge bimetal switch 60, the fuel iiowingfrom the pilot burner I8 is ignited, causing the ballast resistor 40. 56 to become heated in response thereto. It is intended that when this occurs, the relay 34 will l release armatures -42 to open contacts 52- 54 and 48-50; rst, to remove the short-circuit from the electromagnetic valve I6 and; second, to deenerglze the igniting means 22 and cause lthe pilot light 10 to Ibecome lighted. It will be apparent, therefore, that therelay 34 is subject I8 which is normallyclosed. As the main switch combined .with the main fuel valve I4 is also operated to closed position when the main fuel valve is opened, the electrical circuit is established as follows: From the secondary of the transformer 32 to wire 84, wire 86, coil 38 of the relay 34,*wire 88, wire 80, ballast resistor 56, wire 92, heater coil 94 `of the safety bimetal switch 1-4, and wire 96 back to the secondary of the transformer 32.l This circuit remains energized as long as the apparatus is in operation, provided there are no power" supply or electric circuit failures.

A second circuit consists of the secondary of the transformer 32, wire 9 8, pilot signal light 10, Wire |00, fixed relay contact 48, movable relay contact 414, armature 42, wire |02 and wire |04 back to the secondary of the transformer 32.'` This circuit is established for the short interval Abetween the closing of the main switch of valve |4 (when lot signal light 1li!Y to light.

Energizvation of the coil-88 of the` control relay 34 in the first circuit described will attract the armatures 40-42 and cause engagement of to two conditions. The rst, is that it obtain sufficient electrical energy to pick up the armatures 40-,42 when the circuit elements are cold. The second is that it avoid introducing a sufliciently large resistance in series with the ballast resistor 56 which would unduly retard the release of the relay armatures when the ballast resistor `becomes heated by the ame of the vpilot burner I8.

In order to assure release of the armatures and consequent dropping of the relay contacts under heated conditions of the circuit elements and also to assure attraction of the armatures and incidental closing of therelay contacts under cold circuit conditions, means are provided in this invention to add exibility to the adjustment of the relay circuit without materially affecting the sensitivity of the relay to changes in resistance of the ballast resistor which are caused by variations in the condition of the pilot burner, such as the lighted and unlighted conditions l thereof.

To this end, a shunting resistor |28 is connected across the coil 38 of the relay 34 by wire |30 connected to wire 86, and by wire |32 `connected to wire 88.` A cut-out |34 may be included in the shunt as by connection between wire |32 and wire 88. The cut-out |34 is preferably lof the thermal type having a time lag operation and will open the l circuit in case of failure of the relay circuit as by becoming open circuited. It will be apparent,

however, that a cut-out will be unnecessary if the shunting resistor |28 is securely-.connected directly across the relay coil to render such an open circuit remote.

However, if the cut-out |34 is included, the relay coil 38 in its normal v i condition would require an appreciable current resistor 56 and renders the circuit sensitive to the changes in resistance of the ballastv resistor responsive to the flame of the pilot burner. Thus, the ballast resistor 56 is enabled to control operation of the relay 34 by varyingthe total circuit resistance in response to'thermal changes caused by operation of the pilot burner, thereby'varying the electrical energyvalue to the relay coil 38. After the pilot burner flame 8 has sufficiently heated the ballast resistor 56 the resistance of this ballast resistor is increased, the voltage to relay coil 38 isdecreased to armature release value and the armatures 40 and 42dropv ytheir contacts 52 and 48, respectively.

As outlined in the preceding paragraph, the relay 34 is caused to release the armatures 46 and 42 when the ballastl resistor 56 is suiiiciently heated. This action is'due to the decreased (IR) voltage drop across the resistor |28 when the resistance value of the ballast resistor 56 increases with temperature. As disclosed herein, thevoltage source for the control circuits of the burner apparatus is supplied by the secondary winding of the transformer, 32; the output of this secondary being connected across its terminals and comprising the described series circuit including heater coil 94, resistor 56 and the shunt circuit including resistor |28 and coil 38. It is apparent that the total current in the series path proportionately divides in the parallel path. The resultant impedance of the resistor |28 and coil 38 in parallel is less than the impedance ofl coil 38 alone. Moreover, as resistor 56 varies'the cur.- rent value in the circuit, the voltage` drop across resistor |28 varies correspondingly and this (IR) voltage drop serves in effect as the voltage source for the coil 38. v

The opening of contacts 52-54 and 4,8--50 occurs simultaneously with,.closing of contacts- 44-46. The opening of contacts 48- 50 discontinues the described`circuit controlled thereby and causes deenergization of the ignitionmeans cut-out A6.4, -66to be openedand thenormaly running'condition ofthe apparatus iisaestablish'eda. 1 a. f' In'theeventlthataboth the main? burner and the pilot"burneri'ilameslA are extinguished?, the system `willzrecycle.` l.'I'hel-flamesensitive'ballast coil 56 will cool andits resistance willv consequently be -decreased'untilther'e issiifllcient current in the circuitof-the relay coil" 34 to cause the'xarma'tures y4|l-'42 to bei attracted thusclosing 1 contacts 52-54 and'48-"50. IDuring this coolingperiod ofv the ballast resistor* 56 `l`the electromagnetic' valve remainsenergized andconsequently un- '15 total circuit resistance in series withvthe ballast burned fuel willf temporarily 'escape *fromr the 1 -main burnerr 'I 8. However,fas`soonas the contacts 5254`close, the electromagnetic yvalve I6 and` heater coil |24' of the'pufrgebimetal switch 60 become short-clrcuitedL This causesthe valve to close and thfuel'to the main burner I6 to be lshut off while-fthepurge bimetal*switch6|! begins to cool. f-It willfbbbservedthat the closing of contacts 484-58 does riot immediately cause the ignitionme'ans 22 to Hbe energized as the circuit is'still operit'iwingY to 'the purge-bimetal switch contacts6466 being ope'n/ {'Thefcooling kperiod vof the bimetal switch 60 "is arranged tobe vdeilnitely'longe'r than" the `period during which the unburned"main` burner gas escapes. [When the 'purge bimetal 'switchGU c'oolssuciently'to close undergoes a recyclingoperation up tothe point where the ignitng `means ,212.' is energized. The

' system remainsV in vthis condition withthearma- 22; closing of contacts 44--46 completesthede scribed circuit-controlled thereby and' 'causesflthe pilot light 10 to be lighted; and vopening of fcontacts 52--54 as will now be describedremoves the short-circuit and causes the electromagnetic valve I6 to be energized for'movem'ent .to open position permitting flow of fuel". tothe main" y burner I0. This valve energizingvactionoccurs owing to the safety bimetal switchfcontacts 18-80 being closed and the circuit consequently consisting of the transformer secondary 3 2. safety',

bimetal switch contacts 18-80, limiting resistor 82, heater coil |24 of the purge bimetalswitch 6|), wire |22, electromagnetic valvel" 6. andwire |20, back to the secondary ofthe `tra`v`nsfo-rrr1 er 32. It will be observed that theheated. @nml-0n of the purge bimetal switch 68 causes its'contacts and cause the electromagn tures 46,-42 attracted .and the electromagnetic valve I6 closedvuntl fthe'fuel supply isfreestab lished Thesysteim will then continue through the recycling,operation'v previously described..

`In the case'of electric currentjfailure'the fuel to themam' burner hwii1ibeshutcffby' @pei-ation `0f the 4 :sllffelly-. .liielkl-E switch', varid fthe pilot burner. 8 willicontinu'e to .produce a flame.; When thev power suiplyi's realised..thesaretyibimetai sLwitchfMA will closeits conta sl 18e- 86 'causing' the kelectromagnetic .vali/ej i6] y l,begreenergized and admit fuelto, the .rnain burner I0.. Ifthehpilot flame should.. .be eitingui" ed c iuri'ngitf` a power failure, the ,unburri/ed' pilot cape. and thesystem; will co w condition. v,In.they,eveifitotan open circuitbc# curringin theljballast resisto circuit, the safety bimetal switch, `14 wi11;penj S1 patents 18g-sn ic-fvalV, |6to.fclo'se and shut oi the lo'wc'f fuel, he'icnain,burnegri 8.

While a preferred' embodimentiolthc invenftion has `been shown and described, itis lailparerit that many modificationsw'l in the art. Hencthe i -1. mav mule vform shawn anmdsiteafbf etalerwise than-l as included in tliefsl' copevvv of the claims ary circuit including said source of electrical energy, said device, and means for varying thetotal circuit resistance inresponse to thermal changes` said device, and a ballast resistor for varying the total circuit 'resistance in response to thermal changes caused by operation of the pilot burnerthereby varying the energy value to said device to change the position of said movable means.

3. A safety control for fuel burners having main and pilot burners, comprising a main circuit including a source of electrical energy, electrically operable means movable between posicontrolled by one of said devices for maintaining said igniter inoperative for a predetermined period tions for controlling the supply -of fuel to the main burner, an electric ignite;` adapted for operation to ignite the pilot burner, an electrically responsive device for positioning said movable means and controlling the operation of said igniter, and 'aysecondary circuit including said source of electrical energy, said device, anda ballast resistor having a positive temperature coeiiicient of resistance for varying the total circuit resistance in response to thermal changes caused by operation of the pilot burner thereby varying the energyl value to said device to change movable means, of a secondary circuit including the position of said movable means and terminate l operation of said igniter. n 4. A safety control for fuel burners-having main and pilot burners, comprising a main-circuit 4 including a source of electrical energy, electrically operable. means movable between' 1 positions forA .controlling the supply of fuel to the main bur`nex ',v a switch controlling the operation of said movable'H means, an electric igniter adapted for operaticrito ignite the pilot burner, a separate switch conf.

trolling the operation of said igniter, a secondary electrically responsive means for causing oper-,l

ation of said switches, a fixed resistorshunting said electrically responsive means and reducing 6. A safety control for fuel burners having* main and pilot burners, comprising `a main cir'- cuit including a source of electrical energy, electrically operable means movable between positions for controlling the supply of fuel to the main burner, an electric igniter adapted for op eration to ignite said pilot burner, an electrilcally responsive device for positioning said movable means and controlling the operation of said igniter, a secondary circuit including said source of electrical energy, said device, and means for varying the total circuity resistance in response to thermal changes. caused by operation of the pilot burner thereby varying the energy value to A v said device to change the position of said movable means and terminate operation of said igniter, an electric heater controlled by said der vice, and a thermal switch associated with said heater for maintaining said igniter electrically disconnected fromsaid main circuit for a tim period determined by said heater. f

7. In `a safety controlfor fuel burners, the combination with a main ycircuit including a sourcekof electrical energy, electrically operable meansk movable between positions for controlling the supply of fuel tothe burner, an electrically responsive device for controlling the opc eration of said movablemeans, a thermally oper' able device also controlling the operation of said said source of electrical energy, said electrically responsive device, and means for varying the total circuit resistance in response to thermal changes caused by operation of the burner there by varying the energy -value to 'said' electrically responsive device to change the position of said movable means, and an electric heater for said @thermally operable device for causing operation `circuit including said source of electrical energy the effective impedance value ofthe latter in said secondary circuit, and a ballast resistor for varying the total circuit resistance in response to thermal changes caused by operation of the pilot burner thereby varying the energy value to said `electrically responsive means suiliciently to cause said switch operation.

5. A safety control for fuel burners having main and pilot burners, comprising a main circuit including a source of electrical energy, electrically operable means movable between positions for controlling the supply of fuel to the main burner,

an electric igniter adapted for operation to ignite said pilot burner, an electrically responsive device for positioning wsaid movable means and controlling the operation of said igniter, a secondary circuit including said source of electrical energy, said device and means for varying the total cir-A cuit resistance in response to thermalchanges caused by operation of the pilot burner thereby varying the energy value to said device to change the position of said movable means and terminate operation of said igniter, and timing means thereof to change the position of saidmovable means in the event of failure 'of -said secondary 1 1 gcircuit.. f e

8. In a safety responsive device for controlling the operation of said movable means, a thermally operable switch for completing said main circuit and thereby controlling the operation of said movy able means, of a secondary circuit includingsaid source of electrical energy, said electrically responsive device, and means for varying the total circuit resistance in response to thermal changes caused by-operation of the burner thereby varying the energy value to said electricallyvresponsive device to change the position of saidmovv able means, and an electric heater for said switch l adapted to cause operation ythereof to discontinue i said main circuit and change the position of said movable means in the event of deenergization of 'Y said heater by failure of said secondary circuit.

9. A safety control for fuel burners having main and pilot burners and a source of electrical energy, comprising electrically operable means movable between positions Afor controlling the supply of fuel to the main burner, a circuit including the source and said movablemeans, a relay having a coil and a switch operable thereby for changing the position of said movable means,

said switch operation being dependent upon a variation in energy value supplied to said coil,

control for fuel burners, the v.combination with a main ,circuit including a source of electrical energy,.electrically operable` Fmeans movable between positions for controlling the supply of fuel to the burner, an electrically a second circuit including the source, said coil, and a ballast resistor exposed to a flame at the pilot burner for causing said variation in energy value by varying the total circuit resistance when heated by said dame, and means for reducing the effective impedance value of said coil in said second circuit sufciently to render said variation in energy value effective to cause said switch operation. v

10. A safety control for fuel burners having main and pilot burners and a source of electrical energy, comprising electrically operable means movable between positions for controlling the supply of fuel .to the main burner, a circuit including the source and said movable means, a re'- lay having a coil and a switch operable thereby for changing the position of said movable means, said switch operation being dependent upon a variation in energy value supplied to said coil, a second circuit including the source, said coil, and Aa ballast resistor exposed to a ame -at the pilot burner for causing said variation in energy value by varying the total circuit resistance when heated by said flame, and a fixed resistor establishing a shunt on said coil and reducing the eiiective impedancey value thereof in said second circuit suiiiciently to render said variation in energy value effective to cause said switch operation.

11. A safety control for fuel burners having main and pilot burners and a source of electrical energy, comprising electrically operable means movableI between positions for controlling the supply of fuel to the main burner, a circuit including the source and said movable means, a relay having a coil and a switch operable thereby upon a reduction in the energy value supplied to said coil, means controlled by said switch forv short-circuiting said movable means. a second circuit including the source, said coil, and a ballast resistor exposed to a flame at the pilot burner for causing said reduction by increasing the total circuit resistance when heated by said flame, and a fixed resistor establishing a shunt on said coil and reducing the eective impedance value thereof in said `second circuit sufficiently to render said reduction in energy value effective to cause operation of said switch to remove said short-circuit. g

12. A safety control for fuel burners having main and pilot burners and a source of electrical energy, comprising electrically operable means movable between positions for controlling the supply of fuel to the main burner, an electric igniter adapted for operation to ignite the pilot burner, a circuit including the source, said movable means and said igniter, a relay having a coil and separate switches operable thereby for changing the position of said movable means and terminating operation of said igniter, said switch operation being dependent upon a variation in energy value supplied to saig coil, a second circuit including the source,.sa.id coil, and a ballast resistor exposed to a flame at the pilot burner for causing said variation in energy value by varying the total circuit resistance when heated by said flame, means for reducing the effective impedance value of said coil in said second circuit sufliciently to render said variation in energy value effective to cause said switch operation. and means responsive to said switch operation for delaying resumption of said ignite! operation when said switch operation is terminated upon cessation of said name.

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